In order to compensate for the recoil that occurs when shells, projectiles or similar ammunition units are fired from a weapon such as an anti-tank weapon, anti-armour weapon or similar weapon held by a weapon user such as a soldier, an impulse opposing the recoil of the ammunition is needed. If no opposite directed impulse is created, high recoils may occur rendering the weapon unusable to the weapon user for security reasons. Today there are two common ways to create this opposing impulse.
One way of doing this is to arrange a conical nozzle in the rear end of the weapon that ventilates a large amount of gun powder gas and creates a counter force. An example of such a weapon on the market is our recoilless rifle Carl Gustaf. The principle to create the counter force is the same as for a rocket motor.
Another way of doing this is to use a countermass that accelerates backwards in the weapon barrel when the ammunition unit is fired forwards under gas pressure created by gun powder exploding between the ammunition unit and the countermass. In comparison with the nozzle arrangement a smaller amount of gun powder is required for corresponding projectile muzzle velocities. The principle using countermass is today used in our anti-tank weapon AT4 CS and many similar weapon systems worldwide. Examples of recoilless weapon using the countermass principle and embodiments of countermass containers are inter alia known from US 2005217468 A1, US 2006249011 A1, U.S. Pat. No. 6,286,408 B1, US 2005235816 A1 and WO 91/11673 A1.
When using recoilless weapons based on the countermass principle it is likely that symmetry problems occur affecting the hit rate. The symmetry problems may inter alias result in that the countermass is obliquely ejected, that an asymmetrical gas leakage arises around the countermass, and that pressure differences are obtained in the weapon funnel during the firing phase. When comparing the nozzle principle with the countermass principle, it is also normally so that the countermass principle does not present the same repeatability in recoil and hit rate as conventional ammunition based on technique using nozzle and expansion of gas.